I RECENTLY RETURNED A NEW 16" BUSHMASTER HEAVY BARREL UPPER BECAUSE THERE WAS A LARGE ROUGH SPOT IN THE BORE NEAR THE MUZZLE.  I TALKED TO BUSHMASTER AND THEY SAID IT WAS PHOSPHATE IN THE BORE FROM WHEN THE BARREL WAS TREATED.   ANYONE ELSE EVER HEARD OF THIS?

Yes. It happens from not properly plugging the brrel when the barrel is parkerized. Parkerizing is either a zinc phosphate or a manganese phosphate. They should replace the barrel as it will affect accuracy and perhaps barrel life.

That's strange, I've heard that the barrel's finish can't stick to chrome?

Parkerizing will not stick to chrome linings, but, chrome linings are NOT always applied to an even depth and may have 'bald' or bare spots.

I have alot of experience with new BM barrels.

I would estimate that approx 75% of new barrels from BM have phosphate running into the rifling.

THIS IS ANOTHER BUSHMASTER WEAKNESSES.

From my experience, I can tell you that it has never effected accuracy for me.  I normally get 1.0 inch to 1.25 inch groups (five rounds at 100 yards using 20X Leupold) from these flawed barrels stright from the box (virgin barrel stright from BM).

However, the phosphate will "strip" copper from the bullet and cause copper fouling along the phosphate in the barrel.  This is a big PITA !!!!!  I know, I know.... how come the bullet does not remove the phosphate over-coating while firing.  I do not know either.  I can only speculate that the bullet does not have much contact with the barrel between the raised rifling.

I can also tell you from first hand observation that it appears to be phosphate over-coating.  I have examined the muzzle with a 16X Loupe, and I can clearly see that it is phosphate extending into the muzzle.  I agree that it looks like the chome lining failed to be applied evenly, and what you think that you are seeing is the bare steel between gaps in the chrome lining.  But, THIS IS NOT THE CASE.  This was my first reaction the first time I recieved one of these flawed barrels.  But, after examining with the 16X loupe, I could see it was phosphate.  I called BM too when I first discovered this, and they said it was phosphated over-spray from the muzzle not being tightly capped during the coating process.

Everyone of these flawed barrels have ALWAYS produced AT LEAST 1 1/4 inch groups !!!  So, I have since learned to not to worry about the over spray.  But, as I said, it is a PITA becuase it produces copper fouling from the phosphate scrapping the copper from the bullet.  I have learned to soak the barrel in Hoppe's 9 overnight for several nights (appling a fresh coat of Hoppe's each 24 hour period).  PITA !!! just because BM is too lazy to make sure the muzzle is tightly plugged.

G35 I do not repeat rumors, myths or innuendo. I build AR's, and other types of select guns, for a living. I drill, ream and rifle barrel blanks from scratch. I also examine the bores of these barrels with a 'bore scope' from breech to muzzle prior to contouring, threading or chambering. It is my professional experience that phosphate in the bore of a rifle will probably affect accuracy and useful barrel life. That is why I replace any barrel that I parkerize should phosphate leak into the bore. By the way I regard any barrel I build that would only shoot 1 inch to 1.5 inch groups as a failure. Believe what you will. Charles.

1911builder,

Thanks for the reply.  I have retracted (edited) my sly comment.  You do have much more experience than I do.  I am just a casual shooter that has purchased many BM barrels.

Can you help me to understand how the over spray affects the barrel life.  I am asking in an honest manner, and seeking knowledge.  I am not asking in an agruementive manner.  THANKS

I have a 20" cheap barrel I bought years ago that was not chrome lined. It looked as if it was done without even plugging the barrel. It was so bad in the chamber it would not even cycle a round. I polished out the chamber and it works fine now and it fairly accurate. Really suprised me.

That is why I replace any barrel that I parkerize should phosphate leak into the bore. By the way I regard any barrel I build that would only shoot 1 inch to 1.5 inch groups as a failure.

What do you do with these failures?

j3_,

Did yours have excessive copper fouling from the rough phosphate pulling copper from the bullet ?

Did the phoshate ever clean out from firing a lot of rounds over time ?  I never shoot mine enough to ever find out.

Just looking with a light it is still pretty dark in the bore and the chamber. Does have more of a smooth look but still dark I have no way to reallly examine it any better.

G35 I was not attacking anyone. I am by nature and training (22 years USMC, infantry and armorer) a very direct person. That said, when a barrel throat has been subjected to high heat levels and lots of ronds down the bore it exhibits a phenomena known as 'fire cracking'. This looks kind of like dried mud cracks on a dry lake bed. This erosion causes the bullet to yaw upon entering the rifling and the bullet never really recovers or stabilzes.

Parkerizing in the bore exhibits this same type of fire cracking. Gas leaks around the edges of the bullet and it yaws and cannot stabilize in a predictable manner. So parkerizing in the bore tends to affect accuracy. This is not a real problem for most casual shooters, but, serious competitors and fanatic armorer/gunsmiths such as myself are always striving for perfection, and customer satisfaction.

To elaborate, yesterday my client and I went shooting with his Colt HBAR and my new 1 in 8 inch twist Shilen select match barrel inan 18 inch carry handle configuration cahmbered in 5.56 WYLDE. His best group using an ACOG 4 power scope at 100 yards was about 2 inches with the HBAR. His group with my Shilen barrel, using iron sights, standard A2 aperture was small enough to cover 3 shots with a nickel. That was success because the Shilen barrel is not broken in and had no scope.

The failure barrels are few as I use only Shilen Select Match and Krieger blanks. I use them for 'beater' barrels or may sell them as a used product if I am not happy with the accuracy. Sometimes I just cut them up and throw them away. It is the cost of doing business. Semper Fi. Charles the Gunsmith.

Just to clarify...

The over spary in the Bushmaster barrels is Not along the entire length of the barrel.  There is a heavy ridge of phosphate as the phosphate coating rolls over the crown and just starts into the rifling.  From the crown to approx 1/4 inch into the rifling, there is an over spray of phosphate.  The over spray looks just like over spray on a car, very literally.  The overspray has a "fogged" appearance from the crown to approx 1/4 inch into the rifling.  Beyong the 1/4 inch into the barrel, there is No phosphate over spray.

Thanks for the replies.  I never saw this talked about before and thought it must be a rare problem.  I have one other personal Bushmaster and also a department issued one with the same problem.  I guess its not that rare.

Shoot steel jacketed ammo. It should remove the phosphate.

Steel jacketed ammo may also remove the rifling.

That would seem to be the case Tweak. The barrels I parkerize are filled with water after plugging one end. Then I plug the other end and parkerize. I always drill the gas port port AFTER parkerizing so that I do not have to worry about leakage in this hole whichis very difficult to plug. The water in the bore during parkerizing dilutes any parkerizing solution that may get past the breech and muzzle plugs. So far this system has yet to fail.